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''Triceratops'' is a genus of herbivorous ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the late Cretaceous period, about 68 million years ago (Mya) in what is now North America. It is one of the last known non-avian dinosaur genera, and became extinct in the Cretaceous–Paleogene extinction event 66 million years ago. The term ''Triceratops'', which literally means "three-horned face", is derived from the Greek τρί- (''tri-'') meaning "three", κέρας (''kéras'') meaning "horn", and ὤψ (''ops'') meaning "face".〔(【引用サイトリンク】url=http://www.etymonline.com/index.php?term=triceratops&allowed_in_frame=0 )〕 Bearing a large bony frill and three horns on its large four-legged body, and possessing similarities with the modern rhinoceros, ''Triceratops'' is one of the most recognizable of all dinosaurs and the best known ceratopsid. It shared the landscape with and was probably preyed upon by the ''Tyrannosaurus'', though it is less certain that the two did battle in the manner often depicted in traditional museum displays and popular images. The exact placement of the ''Triceratops'' genus within the ceratopsid group has been debated by paleontologists. Two species, ''T. horridus'' and ''T. prorsus'', are considered valid, although many other species have been named. Research published in 2010 suggested that the contemporaneous ''Torosaurus'', a ceratopsid long regarded as a separate genus, represents ''Triceratops'' in its mature form. The view was immediately disputed〔〔(), Longrich NR, Field DJ (2012) Torosaurus Is Not Triceratops: Ontogeny in Chasmosaurine Ceratopsids as a Case Study in Dinosaur Taxonomy. ''PLoS ONE'' 7(2): e32623. 〕〔(), Bowdler, Neil(1 March 2012).'' ''Triceratops'' has been documented by numerous remains collected since the genus was first described in 1889, including at least one complete individual skeleton.〔 Paleontologist John Scannella observed: "It is hard to walk out into the Hell Creek Formation and not stumble upon a ''Triceratops'' weathering out of a hillside." Forty-seven complete or partial skulls were discovered in just that area during the decade 2000–2010. Specimens representing life stages from hatchling to adult have been found. The function of the frills and three distinctive facial horns has long inspired debate. Traditionally these have been viewed as defensive weapons against predators. More recent theories, noting the presence of blood vessels in the skull bones of ceratopsids, find it more probable that these features were primarily used in identification, courtship and dominance displays, much like the antlers and horns of modern reindeer, mountain goats, or rhinoceros beetles. The theory would find additional support if ''Torosaurus'' was found to be the mature form of ''Triceratops'', as this would mean the frill also developed holes (fenestrae) as individuals reached maturity, rendering the structure more useful for display than defense.〔 ==Description== Individual ''Triceratops'' are estimated to have reached about 7.9 to 9.0 m (26.0–29.5 ft) in length, in height,〔(【引用サイトリンク】title=T Dinosaurs Page 2 )〕〔(【引用サイトリンク】title=Triceratops in The Natural History Museum's Dino Directory )〕 and 6.1–12.0 tonnes (13,000–26,000 lb) in weight. The most distinctive feature is their large skull, among the largest of all land animals. The largest known skull (specimen MWC 7584, formerly BYU 12183) is estimated to have been in length when complete,〔 and could reach almost a third of the length of the entire animal.〔 It bore a single horn on the snout, above the nostrils, and a pair of horns approximately long, with one above each eye. In 2010, paleontologists revealed a fossil (named "Yoshi's Trike" MOR 3027) with 115 cm long horn cores, housed and displayed at the Museum of the Rockies in Montana. 〔http://msuexponent.com/news/2012/10/04/yoshis-trike-on-display-at-museum-of-the-rockies/〕〔John B. Scannella, Denver W. Fowlera,b, Mark B. Goodwinc, and John R. Horner, (Evolutionary trends in Triceratops from the Hell Creek Formation, Montana ), June 2015.〕 To the rear of the skull was a relatively short, bony frill, adorned with epoccipitals in some specimens. Most other ceratopsids had large fenestrae in their frills, while those of ''Triceratops'' were noticeably solid. The skin of ''Triceratops'' was unusual compared to other dinosaurs. Skin impressions from an as-yet undescribed specimen show that some species may have been covered in bristle-like structures, similar to the more primitive ceratopsian ''Psittacosaurus''.It is assumed that juveniles may have bristles, then shed the bristles and expressed only scales as the animal became larger and no longer needed insulation to stay warm. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「triceratops」の詳細全文を読む スポンサード リンク
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